Interventional catheter-assisted aortic valve implantation is a method for treating patients suffering from high-grade aortic valve stenosis. Here, similarly to a cardiac catheter examination, the implantation is performed via the artery in the groin (transfemorally), a small incision in the left-hand side of the chest above the apex of the heart (transapically) or via an upper partial sternotomy directly through the aorta (transaortally) of the patient. At the beating heart, the constricted, natural aortic valve is first expanded using a balloon (balloon valvuloplasty) and a vascular prosthesis with integrated biological heart valve is then introduced via a catheter and unfolds for implantation at the location of the diseased aortic valve.
In order to achieve this functionality, such a catheter device for aortic valve implantation typically has an outer catheter tube with a distal end and a proximal end and has an inner catheter tube guided therein at a radial distance in a manner displaceable relative thereto. Due to the relative movement of the two catheter tubes, a specific function of the catheter device can be implemented, such as the exposure of the balloon for expansion of the natural heart valve or the implantation of the actual valve prosthesis by release of the vascular prosthesis.
A typical conventional heart valve prosthesis consists basically of a main structure and a heart valve fastened and integrated therein. The heart valve itself may consist here of natural tissue (such as pericardium tissue from a pig or cow) or polymer tissue (Dacron or the like). Donor valves are also possible. The heart valve is fastened in the main structure, wherein it is usually sewn to the main structure. The main structure serves to anchor the vascular prosthesis at the location of the natural valve. The main structure is basically a stent and can be either self-expanding or expandable by a balloon. In the case of a catheter system of the type mentioned in the previous paragraph, the vascular prosthesis is covered by the outer catheter tube during the insertion and positioning at the site of implantation. The outer catheter tube is retracted for the implantation. In the case of a self-expanding main structure, the force that holds the main structure in its compressed state on the inner catheter tube is cancelled by retracting the catheter tube. The main structure thus expands and anchors at the location of the natural heart valve. In the case of a balloon-expandable main structure, this is exposed and can be expanded by retracting the outer catheter tube.
A problem with aortic valve implantation is caused by the catheter device being tightly curved in the aortic arch. This can create problematic friction between the outer and inner catheter tube. In particular, the increase in friction caused by the curvature can cause the catheter tubes to move stiffly relative to one another, and therefore the controllability of the catheter functions may be impaired.
The prior art discloses some solution approaches to this problem. It is known from US 2006/0229574 A1 in conjunction with catheter lumens sitting one inside the other to provide bumps and indentations on a surface that comes into contact with other catheter surfaces. The friction of such an undulating surface with a smooth surface lying thereagainst is reduced on the whole, and therefore a number of catheter tubes can move smoothly relative to one another.
EP 1 459 706 A1 discloses a method for applying a self-expanding stent to a catheter, where at least one of the involved components—that is to say the stent itself, corresponding mechanism for compression of the stent, the involved transfer tube or the catheter itself—is provided with a sliding coating consisting of a biocompatible lubricant in order to reduce the friction encountered with components movable relative to one another. A glycerol-containing lubricant is mentioned as a preferred example for such a lubricant.
It is known from EP 0 747 073 A1 to provide the outer surface of the inner catheter tube of a medical catheter device and the inner surfaces of the outer catheter tube thereof with a fluid layer in order to overcome the problems concerning friction from the inner catheter tube to the outer catheter tube in the event of a relative movement. In this context, the use of materials having a low coefficient of friction, such as PTFE, or the application of a lubricant, for example in the form of a hydrogel, is mentioned as being known. In addition, this document teaches the application of a permanent fluid layer in the form of a heparin-containing hydrogel.
A delivery system for a self-expanding artificial heart valve with use of a rolling membrane is presented in WO 2010/033698 A1. Here, the friction between the catheter sleeve and the heart valve to be implanted is considerably reduced by the process of rolling the rolling membrane over mechanical paths. Such a rolling membrane can only be used, however, at the end of a catheter device.
US 2011/0213303 A1 discloses a catheter that causes what is known as a “goose bump”—like surface structure for drastic reduction of the friction of the surface formed in this way. The “goose bump” structure is produced by use of a thermoplastic material in the form of polyamide and an elastomer, such as a polyester block amide, in which microscopic particles, such as glass beads, are embedded at the surface. The friction coefficient that can be achieved as a result is compared with that of PTFE.